Asymmetric cation non-stoichiometry in spinels: site occupancy in Co2ZnO4 and Rh2ZnO4
Two cations A and B in A₂BO₄ spinels appear in precise 2:1 Daltonian ratio ("line compounds") only at very low temperature. More typically, at finite temperature, they tend to become either A rich or B rich. Here we survey the experimentally observed stoichiometry asymmetries and describe the first-principles framework for calculating these. Defect calculations based on first principles are used to calculate the enthalpies of substitution of A atom ΔH(ATd) and B atom ΔH(BOh) and determine their site occupancies leading to (non)-stoichiometry. In Co₂ZnO₄, the result of the calculation for site occupancy compares well with that measured via anomalous x-ray diffraction. Further, the calculated phase boundary also compares well with that measured via Rietveld refinement of x-ray diffraction data on bulk ceramic sintered samples of Co₂ZnO₄ and Rh₂ZnO₄. These results show that Co₂ZnO₄ is heavily Co nonstoichiometric above 500 °C, whereas Rh₂ZnO₄ is slightly Zn nonstoichiometric. We found that, in general, the calculated ΔH(ATd) is smaller than ΔH(BOh), if the A-rich competing phase is isostructural with the A₂BO₄ host, for example, A₂AO₄, whereas B-rich competing phase is not, for example, BO. This observation is used to qualitatively explain nonstoichiometry and solid solutions observed in other spinels.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Center for Inverse Design (CID)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1065642
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 84, Issue 6; Related Information: CID partners with the National Renewable Energy Laboratory (lead); Colorado School of Mines; Northwestern University; Oregon State University; SLAC National Accelerator Laboratory; University of Colorado; ISSN 1098-0121
- Publisher:
- American Physical Society (APS)
- Country of Publication:
- United States
- Language:
- English
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